The invention relates to hydraulic transmissions of the type in which the speed of operation of a dispensing apparatus driven by the transmission is made to vary in proportion to variations in a command value furnished by a command device.
More specifically, the invention relates to hydraulic transmissions of the type in which the speed of operation of a dispensing apparatus driven by the transmission is kept proportional to a command value, despite variations in the command value.
Still more specifically, the invention relates to dispensing apparatuses, for example salt spreaders, mounted on vehicles, wherein the transmission which drives the dispensing apparatus is caused to operate at a speed proportional to the vehicle speed, despite variations in the vehicle speed. In the case of salt spreaders, or the like, the maintenance of the relationship just mentioned is particularly important, because it ensures that the amount of salt spread per unit surface area of the roadway will remain substantially constant, irrespective of the speed of the salt-spreading vehicle.
One known transmission arrangement of this type makes use of a hydraulic pump driven by a wheel of the vehicle. The pump draws hydraulic fluid out of a tank and supplies such fluid, via a flow restrictor, to a constant-output pump. The constant-output pump, in turn, supplies driving fluid to hydraulically driven apparatuses mounted on the vehicle. With this arrangement, the constant-output pump is supplied with driving fluid at a volumetric rate proportional to the vehicle speed, by supplying fluid to the constant-output pump in dependence upon the rotary speed of the vehicle wheel and in dependence upon the flow-restricting action of the restrictor. This known arrangement is of relatively simple construction although unfortunately it has proved unreliable in actual use.